In the first part of this paper we investigate how scientific theories can be represented by frames. Different kinds of scientific theories can be distinguished in terms of the systematic power of their frames. In the second part we outline the central questions and goals of our research project. In the third and final part of this paper we show that frame-representation is a useful tool in the comparison of the theories of phlogiston and oxygen, despite those theories being traditionally (...) conceived as incommensurable. The frame-theoretic representation reveals common attributes, values and ultimately structural correspondence relations between the two theories. In our view this outcome lends credence to a structural realist view of science. (shrink)